External and Internal Factors in Evolution 309 
in different localities in color and in length and texture of 
pelage, they do not vary as to the size of their skulls. On 
the other hand the panther (and the ocelots) greatly increases 
in size southward, “ or toward the metropolis of the family.” 
Other carnivora that increase in size northward are the 
badger, the marten, the fisher, the wolverine, and the ermine, 
which are all northern types. 
Deer are also larger in the north; in the Virginia deer the 
annually deciduous antlers of immense size reach their great- 
est development in the north. The northern race of flying 
squirrels is one-half larger than the southern, “yet the two 
extremes are found to pass so gradually one into the other, 
that it is hardly possible to define even a southern and a 
northern geographical race.” The species ranges from the 
arctic regions to Central America. 
In birds also similar relations exist, but there is less often 
an increase in size northward. In species whose breeding 
station covers a wide range of latitude, the northern birds 
are not only smaller, but have quite different colors, as is 
markedly the case in the common quail, the meadow-lark, 
the purple grackle, the red-winged blackbird, the flicker, the 
towhee bunting, the Carolina dove, and in numerous other 
species. The same difference is also quite apparent in the 
blue jay, the crow, in most of the woodpeckers, in the titmice, 
numerous sparrows, and several warblers and thrushes. 
The variation often amounts to from ten to fifteen per cent 
of the average size of the species. 
Allen also states that certain parts of the animal may vary 
proportionately more than the general size, there being an 
apparent tendency for peripheral parts to enlarge toward the 
warmer regions, 7.¢. toward the south. “In mammals which 
have the external ears largely developed —as in the wolves, 
foxes, some of the deer, and especially the hares — the larger 
size of this organ in southern as compared with northern in- 
dividuals of the same species, is often strikingly apparent.” 
